The present invention relates to power converter apparatus and methods, and more particularly, to clamped converters, asymmetrical half-bridges, and similar power conversion apparatus that use a clamped inductance.
DCxe2x80x94DC converters and other power conversion apparatus often use xe2x80x9cclamped converterxe2x80x9d and xe2x80x9casymmetrical half-bridgexe2x80x9d configurations. A common feature of such devices is the use of a power conversion cycle in which a transformer winding, inductor or other inductance is energized in an xe2x80x9conxe2x80x9d phase by application of an input voltage (directly or via magnetic coupling) and then xe2x80x9cclampedxe2x80x9d during an xe2x80x9coffxe2x80x9d phase using a capacitor and/or other circuitry that receives magnetizing energy from the inductance. Examples of such converter configurations may be found in U.S. Pat. No. 4,441,146 to Vinciarelli; U.S. Pat. No. 4,959,764 to Bassett; U.S. Pat. No. 5,291,382 to Cohen; xe2x80x9cSmall-Signal Modeling of Soft-Switched Asymmetric Half-Bridge DC/DC Converter,xe2x80x9d by Korotkov et al, IEEE Applied Power Electronics Conference, Record, 1995, p. 707-711.
Many conventional clamped converter and asymmetrical half-bridge designs use a capacitor to receive energy during the xe2x80x9coffxe2x80x9d phase. A potential drawback of such circuits is that an abrupt change in the converter""s duty cycle can lead to an incomplete energy transfer during the xe2x80x9coffxe2x80x9d phase due to premature entry into the xe2x80x9conxe2x80x9d phase. This can lead to undesirably large peak currents in the inductance. For example, in a transformer-type clamped converter, an abrupt change in duty cycle may lead to excessive magnetizing current in the transformer, which can, in turn, lead to saturation of the transformer. In circuits that use a transistor with an integral body diode to switch the clamping circuit, such premature entry into the xe2x80x9conxe2x80x9d phase can also damage the transistor through uncontrolled reverse recovery of the body diode.
In some embodiments of the invention, a power converter apparatus, such as a DCxe2x80x94DC converter, power supply, or the like, includes an input port, an output port, an inductance, a clamping circuit coupled to the inductance and an output circuit coupled to the inductor and the output port. The inductance may include, for example, a transformer winding and/or a discrete inductor. The apparatus also includes a switch operative to control energy transfer between the input port and the inductance. The apparatus further includes a control circuit operative to control the switch responsive to a current in the inductance while current is being transferred between the inductance and the clamping circuit. For example, the control circuit may include a current sensor configured to be coupled in series with the inductance while current is being transferred between the inductance and the clamping circuit and operative to generate a current sense signal indicative of the current in the inductance, along with a switch control circuit operative to control the first switch responsive to the current sense signal. The switch control circuit may be operative to prevent transition of the switch from the first state to the second state until the current sense signal meets a predetermined criterion, e.g., a signal state indicative of a desired current condition, such as a current approximating zero or a current reversal.
In further embodiments of the invention, the switch includes a first switch. The clamping circuit includes an impedance, such as a capacitor, a second switch operative to control current flow between the impedance and the inductance, and a clamping control circuit operative to control the second switch. The second switch may include a transistor that is responsive to a clamping control signal, and a diode, such as a transistor body diode, coupled in parallel with the transistor. A current limiting circuit may be provided to limit current in the second switch. In some embodiments, the current limiting circuit may be asymmetrical, i.e., may provide a variable impedance responsive to the direction of the current between the impedance and the inductance.
In other embodiments of the invention, a power converter apparatus includes an input port, an output port, and an inductance. A first switch is coupled to the input port and the inductance and controls current flow between the input port and the inductance. A second switch is coupled to an impedance and the inductance, and controls current flow between the impedance and the inductance. A control circuit operates the first and second switches in a substantially complementary fashion to provide energy transfer between the inductance and respective ones of the input port and the impedance, and is further operative to control operation of the first switch responsive to a current in the inductance. An output circuit couples the inductance to the output port.
In method embodiments of the invention, a power converter apparatus that transfers energy from a power source to a load by cyclically energizing an inductance is operated. The power source is decoupled from the inductance. The inductance is then clamped while sensing a current therein. The power source is then coupled to the inductance responsive to the sensed current.
Embodiments of the invention may provide significant advantages over convention converter configurations. In particular, by controlling coupling of a clamped inductance to a power source responsive to current in the inductance while it is being clamped, e.g., responsive to a sensed current in the clamping circuit, the present invention may limit peak current generated in the inductance during transient conditions when the charging/clamping cycle of the inductance abruptly changes and, thus, may prevent saturation of the inductance. In some converter configurations, the invention may also reduce damaging effects, such as uncontrolled reverse recovery of switching diodes.